This invention relates to circuit interrupters, and more particularly to the exhausting of the arced gas from the molded case of a circuit interrupter.
A molded case circuit interrupter contains in a single molded housing separable contacts and an operating mechanism for actuating the contacts. It is known that an arced gas generates in the arcing region due to a high temperature electric arc drawn between separating contacts upon the interruption of an undesirable current flowing through a circuit interrupter. As is well known, since the arced gas is undesirable because of its high temperature, high pressure and because it contains ions and metal vapors, it should be exhausted from the housing as quickly as possible.
In order to quickly exhaust the arced gas from the housing, many circuit interrupters have an exhaust passage formed in the housing wall other than the bottom wall. One example of such a circuit interrupter is disclosed in Japanese Patent Laid-Open No. 57-180837 in which the arced gas generated in the arcing region between the separated contacts is exhausted through an exhaust passage formed in the cover section of the housing having perforated baffle plates after passing through a pressure-reducing space. This circuit interrupter, similarly to other conventional circuit interrupters, has its exhaust passage in the cover portion or the upper portion of the housing, and the single compartment defined by the housing wall for containing the contacts and the operating mechanism. Therefore, the arced gas generated in the arcing region travels through the single compartment in which the operating mechanism is disposed toward the gas exhaust passage. Since the arcing region and the operating mechanism are usually enclosed in a common single compartment defined by the housing, the arced gas flowing toward the exhaust passage inevitably diffuses toward the operating mechanism to contact with the metallic elements of the mechanism. When the metallic vapor entrained in the arced gas deposits on electrically insulating elements, such as a cross bar, of the operating mechanism, the dielectric strength of the insulating cross bar is degraded, raising the risk of short-circuiting between the poles. Also, when the metallic vapor deposits on the mechanical elements of the operating mechanism, the movement of the elements may be impeded, resulting in a failure of the current interruption. Further, since the outlet end of the gas exhaust passage opens upwardly in the top wall of the housing, the exhausted arced gas can reach the operating handle which is operated by a human hand. Also it is very desirable to have the dimensions of the gas exhaust passage vary according to the desired class of interrupter.